.".us STUDIES IX IMMUNITY. 



whether a given alexin reacts with various cells such as bacteria and 

 corpuscles. In 1895 I thought to outline the process of immuniza- 

 tion as follows: 



"The bactericidal substance (alexin) is the same whatever be 

 the bacterium in question. In animals vaccinated against certain 

 infections the energy of the bactericidal substance is more markedly 

 evident against a particular bacterium, owing to the effect of the 

 preventive substance (sensitizer) which varies in each case and the 

 nature of which depends on the micro-organism used for immuniza- 

 tion. It is owing to the intervention of this particular substance, 

 the specific antibody, that the animal body directs its destructive 

 power against a particular infective agent." 



Is this statement still accurate in spite of the affirmations to the 

 contrary as regards a multiplicity of alexins which have come from 

 Ehrlich in particular? At that time I expressed in a definite man- 

 ner the opinion which was later confirmed by a study of hemolytic 

 sera, that the animal body does not contain a series of alexins, 

 some of which act in the presence of certain sensitizers and are thus 

 employed in struggling against certain bacteria, while others are 

 better adapted to work with other sensitizers to combat other bac- 

 teria. On the contrary it is the same weapon in each instance, 

 a single alexin which reacts now against one and now against 

 another bacterium, owing to the specificity of the sensitizer. Sev- 

 eral of my articles, particularly the one on cytolytic sera in 1901, 

 gave the experimental foundation for this conception, and I may 

 content myself simply w T ith recalling them. 



If this conception w r ere incorrect, if, for example, the hemolytic 

 alexin differed from the bacteriolytic alexin, how would Gengou and 

 I have been able to devise an invariable method for demonstrating 

 anti-bacterial sensitizers, namely, the fixation of the alexin by sensi- 

 tized bacteria, as shown by using sensitized red blood cells as a 

 reagent? Would this method have been universally accepted as it 

 has been? Should we have been able to use it as an argument in 

 favor of the authenticity of our organism of whooping cough? If the 

 conception, which is the basis of this method, were false, what con- 

 fidence would remain in the serum diagnosis of syphilis? Notwith- 

 standing, the contrary thesis of a multiplicity of alexins in a given 

 serum met with the support of many investigators a few years ago. 



